Camshaft adjusters are used in internal combustion engines for varying the control times of the combustion chamber valves, in order to be able to variably shape the phase relation between a crankshaft and a camshaft in a defined angular range between a maximum advanced position and a maximum retarded position. The adjustment of the control times to the current load and rotational speed reduces consumption and the emissions. For this purpose, camshaft adjusters are integrated in a drive train by which a torque is transmitted from the crankshaft to the camshaft. This drive train can be formed, for example, as a belt drive, chain drive, or gearwheel drive.
In a hydraulic camshaft adjuster, the driven element and the drive element form one or more pairs of pressure chambers that act opposite each other and can be pressurized with hydraulic medium. The drive element and the driven element are arranged coaxially. By filling and emptying individual pressure chambers, a relative movement is generated between the drive element and the driven element. The spring causing rotation between the drive element and the driven element forces the drive element in a preferred direction opposite the driven element. This preferred direction can be in the same direction or the opposite direction relative to the direction of rotation.
One structural type of hydraulic camshaft adjuster is the vane cell adjuster. The vane cell adjuster has a stator, a rotor, and a drive wheel with external teeth. The rotor is constructed as a driven element that can usually be locked in rotation with the camshaft. The drive element includes the stator and the drive wheel. The stator and the drive wheel are locked in rotation with each other or are alternatively formed integrally with each other. The rotor is arranged coaxial to the stator and within the stator. Together with their vanes extending in the radial direction, the rotor and the stator form oil chambers that act in opposite directions and can be pressurized by oil pressure and allow a relative rotation between the stator and the rotor. The vanes are formed either integrally with the rotor or the stator or are arranged as “inserted vanes” in grooves of the rotor or the stator provided for this purpose. The vane cell adjusters further have various sealing covers. The stator and the sealing covers are secured with each other by several threaded connections.
Another structural type of hydraulic camshaft adjuster is the axial piston adjuster. Here, a displacement element is shifted in the axial direction by the oil pressure, wherein this displacement element generates a relative rotation between a drive element and a driven element via helical teeth.
The control valves of the hydraulic camshaft adjuster control the flow of hydraulic medium between the camshaft adjuster and the oil pumps or the oil reservoir (tank).
The control valve has a housing and a control piston. Within the housing of the control valve there is the control piston. The control piston can move in the axial direction and is guided by the housing. Thus, the control piston can be positioned relative to the housing in any axial position. The positioning is realized by an electromagnet that contacts, with its actuation pin, one end of the control piston and can move the control piston. A spring secures the contact between the control piston and the actuation pin. Through the axial positioning of the control piston, the different connections of the control valve are connected hydraulically to each other or separated from each other and thus can communicate with each other or not. For guiding the hydraulic medium between the connections, the control piston and housing are provided with openings, e.g., grooves and/or holes. The control piston has control edges that control the flow rate together with the edges of the openings of the housing. The control edges themselves are the edges of the respective opening, e.g., grooves, of the control piston. For controlling the flow rate, the edges of the openings of the housing and the control edges are positioned relative to each other such that an opening of the housing stands largely opposite an opening of the control piston and forms a variable flow rate area for the hydraulic medium by the ability to position the control piston.
A central valve constructed as a control valve is arranged coaxial to the axis of symmetry or rotation of the camshaft adjuster or the camshaft. In addition, the central valve is placed within the camshaft adjuster, i.e., the central valve and camshaft adjuster are built one on top of the other in the radial direction. Optionally, between the camshaft adjuster and the central valve there can be the camshaft. The housing of the central valve can be formed as a central screw, by which the camshaft adjuster is locked in rotation with the camshaft. The electromagnet is arranged as a central magnet largely flush with the central valve and is arranged usually fixed on a frame, in particular, on the cylinder head.
Alternatively, a control valve with an electromagnet fixed rigidly on this valve could be arranged on any position in the hydraulic medium circuit outside of the camshaft adjuster and the camshaft and could control the hydraulic medium flow.
DE 10 2008 049 052 A1 discloses a valve with a filter for capturing foreign matter in the hydraulic medium, here oil. The filter thus should prevent the entrance of foreign matter into the valve. Furthermore a filter band is disclosed that has a band-shaped frame element. On the surface of the frame element there are several grooves spaced apart from each other.
WO 2011/032539 shows a filter for liquid or gaseous medium. The filter has a frame that is present as a ring in the closed state. The frame has an advantage of first and second sections with differing material strengths or thicknesses.